Two-dimensional PIC simulations of ion-beam instabilities in Supernova-driven plasma flows

Abstract

Supernova remnant (SNR) blast shells can reach the flow speed $v_s=0.1c$ and shocks form at its front. Instabilities driven by shock-reflected ion beams heat the plasma in the foreshock, which may inject particles into diffusive acceleration. The ion beams can have the speed $v_b\approx v_s$. For $v_b\ll v_s$ the Buneman or upper-hybrid instabilities dominate, while for $v_b\gg v_s$ the filamentation and mixed modes grow faster. Here the relevant waves for $v_b\approx v_s$ are examined and how they interact nonlinearly with the particles. The collision of two plasma clouds at the speed $v_s$ is modelled with particle-in-cell (PIC) simulations, which convect with them magnetic fields oriented perpendicular to their flow velocity vector. One simulation models equally dense clouds and the other one uses a density ratio of 2. Both simulations show upper-hybrid waves that are planar over large spatial intervals and that accelerate electrons to $\sim$ 10 keV. The symmetric collision yields only short oscillatory wave pulses, while the asymmetric collision also produces large-scale electric fields, probably through a magnetic pressure gradient. The large-scale fields destroy the electron phase space holes and they accelerate the ions, which facilitates the formation of a precursor shock.

15 pages, 11 figures, accepted for publication in Plasma Physics and Controlled Fusion

References in corpus (2)

• Gamma-ray bursts and collisionless shocks
• Cosmic Rays X. The cosmic ray knee and beyond: Diffusive acceleration at oblique shocks

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• Collisionless plasma interpenetration in a strong magnetic field for laboratory astrophysics experiments
• Characteristics of solitary waves in a relativistic degenerate ion beam driven magneto plasma
• The interplay of the collisionless nonlinear thin-shell instability with the ion acoustic instability